1. Field of the Invention
The invention relates to a ceramic sintered material for prostheses or implants and also to an artificial joint of a prosthesis, in which at least one joint partner consists of this ceramic material.
2. Description of the Related Art
It is only possible to use a few materials for prostheses with artificial joints on account of the compatibility that is required with human or even animal tissue, the so-called biocompatibility, and the high level of frictional loading of the joint partners. Of metallic materials, titanium-based alloys, for example TiAl6V4, TiAl6Nb7, and cobalt-chromium (CoCrMo) have proved good. Of plastics materials, in particular polyethylene is used for the sockets of the hip-joint endoprostheses and aluminium oxide and zirconium oxide are the ceramic materials that can be used. Whilst prostheses made of merely one of the materials that have been mentioned do not raise any problems in human or animal tissue, the materials cannot be combined together one with the other in an arbitrary manner if friction pairings result, as is the case in artificial joints. Moreover, the presence of the body fluid as a corrosive medium is to be taken into account.
In joints, pairings of joint partners of aluminium oxide, as is the case, for example, in hip-joint endoprotheses, have proved to be particularly good. Both the ball and the socket are made of the same ceramic material. As is known from the publication xe2x80x9cFrettingkorrosion, ein Problem bci Hxc3xcftendoprothesenxe2x80x9d by Frxc3xch, Willmann and Pfaff fErom xe2x80x9cBiomaterialsxe2x80x9d, 18 (1997), No. 12, pages 873 to 876, joint partners of aluminium oxide and of zirconium oxide cannot be paired together, because wear that cannot be tolerated occurs as a result. Even a pairing of joint partners of zirconium oxide is not possible on account of the wear.
It is however, possible to produce with zirconium-oxide ceramic materials work-pieces which, gives comparable dimensions, have a comparatively high level of reliability in particular against comparatively high alternating loads. For this reason, for example, it is not expedient to produce the ball-head diameters of hip-joint endoprostheses below 28 mm in diameter out of aluminium oxide. Diameters below 28 mm with the required levels of strength and endurance strength under alternating repetition of loads can, however, be realized in a problem-free manner with ceramic materials made from zirconium oxide. The disadvantage, however, lies in the fact that balls of zirconium-oxide ceramic material cannot be positioned against sockets made of aluminium oxide and zirconium oxide. It is therefore usual to position balls of zirconium oxide in sockets of polyethylene, although this causes particle-abrasion of polyethylene and thus results in medical problems.
The object of the present invention is therefore to put forward a material, and with that possible pairings of material, for prostheses with joint partners of ceramic materials, whereby new structural configurations with optimum wear characteristics are rendered possible.
According to one aspect of the present invention, there has been provided an artificial joint for a prosthesis, comprising (a) a first joint partner; and (b) a second joint partner cooperating with the first joint partner; wherein at least the first joint partner is made of a sintered material consisting essentially of zirconium oxide and 0.1 to 40% by weight aluminum oxide.